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Medieval recipes for gunpowder produce nearly the same firepower as today's manufactured equivalent, according to recent weapons tests, providing clues as to how the British fleet became one of the largest fighting forces in the world.

He and colleagues recreated the gunpowder - essentially a mixture of sulphur, charcoal and saltpetre - from scratch. They harvested raw sulphur from the hills of Iceland and burned alder wood in the ground to create charcoal. The third ingredient, saltpetre, was obtained from the nitrates left over from manure collected from stables.

The medieval gunpowder was packed into a replica Loshult gun, a small canon-like gun from Sweden which dates from the 14th Century. The newly made medieval gunpowder was able to fire a lead ball as far as 945 metres (and reaching speeds up to 200 m per second), compared to a distance of 1100 metres for the commercial gun powder.

The old recipes called for mixed powder to be 'stamped' - put under pressure - for at least 20 hours, but preferably 30. But even with very little preparation time the team achieved surprising results.

"These simplified powders were unbelievably effective," Smith said. "What stunned us is if you take these simple ingredients and mix them together for five minutes, it goes off like an absolute rocket."

The team also loaded larger guns with the same simple mixture and fired them at thick wooden walls to simulate firing on ships at sea. They found that guns loaded with stones made a fist-sized hole in the side of the wooden wall, while cast iron balls blasted a hole larger than themselves.

Next, the group will try out different ratios of the ingredients in the gunpowder to recreate how people might have tried to improve it during the first few centuries of its existence.

"In the evolution of combat, it's always a race between attack and defence," Smith said. "Knowing how effective these guns were will give us information on how people decided to go about building castles, fighting wars and even building their ships. After all, the reason the U.K. got where it did was largely because of its navy."